The present invention provides an accurate technique for continuously making on-machine measurements, on selected off-machine measurements of low coat weights applied to paper in the range where conventional methods such as the beta gauge technique or the coating consumption technique have proven to be inaccurate and unreliable. The beta gauge technique is fully described in U.S. Pat. Nos. 3,019,336 and 3,130,303, however, the percentage of error of coat weights in the range of from about 0 to 5 pounds per ream has been found to be large with the beta gauge method. Coat weights as measured by the coating consumption technique are reasonably accurate, but the results obtained only yield an average coat weight over a given period of time with no indication of coat weight variation on the web in either the cross direction or machine direction of the web. Of course there are other known methods of measuring coat weights applied to a paper web or the like, but they are generally off-machine methods employing a chemical analysis or ash determination.
For the purpose of the present invention a ream of paper is defined as 3300 square feet of paper, or 500 sheets measuring 25 .times. 38 inches.